1. Field of the Invention
This application relates to an improved electrochemical detector cell design and to an improved electrochemical measuring apparatus incorporating the detector cell design. More particularly, it relates to such a cell design and measuring apparatus applicable to electrochemical detection and measurement methods for many different substances that are electro-active at an electrode or that contribute to electrochemical conductivity in liquids. Most especially, it relates to such an electrochemical detector cell and apparatus in which a substance in a gas stream is converted to an electro-active form by thermal methods and then dissolved in a suitable electrolyte for electrochemical detection. The invention further relates to such an electrochemical detector cell and apparatus in which a first gas or liquid fluid stream is mixed with a second liquid stream, and the constituents of the first stream are detected and measured electrochemically.
2. Description of the Prior Art
Coulson et al. in "Analytical Chemistry," 32, 1245 (1960) reported a titration cell for the continuous and automatic titration of chloride by silver coulometry. An apparatus for titration of chloride as well as other titratable reactants was disclosed in Coulson et al., U.S. Pat. No. 3,032,493, issued May 1, 1962. Improved apparatuses for coulometric titration in similar cells were disclosed by Myers et al., U.S. Pat. No. 3,427,238, issued Feb. 11, 1969, and Coulson, U.S. Pat. No. 3,563,875, issued Feb. 16, 1971. No significant improvements in cells have been made since then over the original Coulson et al. design. Even so, sensitivity is limited by the reagent volume in which the titration is accomplished and by the electrical noise level of the driving circuits.
Despite the absence of further significant development in electrochemical detector cell design, the art pertaining to coulometric titration apparatuses is a well developed one. Examples of such prior art apparatuses are disclosed in Liesch, U.S. Pat. No. 3,305,468, which discloses a batch titrator with interruption before the titration end point; Strickler, U.S. Pat. No. 3,308,041, which discloses a titration cell and apparatus incorporating separated compartments and a mixing funnel in the cell; Wickerham et al., U.S. Pat. No. 3,341,430, which discloses a coulometric titration apparatus with on-off cycling; Dahms, U.S. Pat. No. 3,551,109, which discloses coulometric generation of two species in a batch titration; Linblad et al., U.S. Pat. No. 3,647,668, which discloses a four-electrode coulometric titration cell and apparatus; Muto et al., U.S. Pat. No. 3,846,270, which discloses a membrane flow through coulometric detector cell with three electrodes; Hauser, U.S. Pat. No. 3,912,613, which uses a two-electrode cell with alternating generating and sensing functions; Arawa et al., U.S. Pat. No. 3,950,237, which describes a four-electrode batch type titrator with improved means of integrating the generation current; Fletcher et al., U.S. Pat. No. 4,018,565 describes a four-electrode process titration system with means for automatic introduction of reagents into the titration cell and for circulating titration constituents; Buzza et al., U.S. Pat. No. 4,007,105 which describes a four-electrode cell with amperometric detection; Wilson, U.S. Pat. No. 4,055,478 describes a batch four-electrode titrator with an antilogarithm converter to control the reagent generator current; Mansfield, U.S. Pat. Nos. 4,066,528 and 4,111,776 describes the use of an instrumentation amplifier with a selectable offset bias connected to the sensor and reference electrodes to control the rate of titrant generation in a batch type cell; Victor et al., U.S. Pat. No. 4,118,300 describes a batch four-electrode cell with antilogarithmic control of the generation current; Moore, U.S. Pat. No. 4,133,733 describes a four-electrode coulometric titration cell without provision for continuously changing the electrolyte contained therein; Buzza et al., U.S. Pat. No. 4,170,523 describes a four-electrode batch cell with amperometric sensing electrodes; Ishikawa, U.S. Pat. No. 4,203,156 describes a three-electrode batch type with chopped signal and generator circuits; and Blanke, U.S. Pat. No. 4,230,554 describes a four-electrode batch cell with amperometric sensing electrodes.
Thus, while the art relating to electrochemical detector cells and apparatus incorporating such cells is a well developed one, further improvements are required in order to meet performance demands for certain applications. Such cells need a high level of sensitivity, a rapid response time, and the ability to be convertible for different species to be measured if they are to be employed in combination with gas or liquid chromatographs.